Air bubbles are completely unacceptable anywhere in the fuel system. There is an air leak somewhere in the remote needle valve assembly, which is probably what is causing the problem.

We had a similar issue with a student's OS .40LA, lots of bubbles in that line, and even though everything LOOKED OK on a visual inspection, the tubing between the remote needle and the carb had a pinhole that was only visible if you completely removed the tubing and stretched it out. Replacing the tubing fixed the issue.

Say what you will about OS, but the after-purchase support you get from Hobby Services is hard to beat. If you can't get it sorted out in a reasonable amount of time, send it to them with a nice note describing the issue. Might cost you a couple of weeks of flying that particular plane, but better than the alternative of not flying the plane at all.